text:
Is there a height limit to national airspace?
Given the following facts:

satellites can operate at an altitude of 200km without triggering frontier violation incident
aircraft can trigger diplomatic protestations if they cross a frontier at an altitude of few kilometers
there is a gap between high altitude and space

There must be a altitude or height limit between national and international airspace. If so, what is this limit?

Related: How high must a craft fly in order to not be in foreign airspace?. However this should be asked to layers rather than aviators, since obviously there is a gap in international laws. Also interesting The Vertical Limit of State Sovereignty mentioning the case of launching and returning spacecraft to/from outer space which means crossing national airspaces for many States.

In most cases the answer is: What's the range lmit of your AA defense system (interceptors included)? =)

It should be also said that the actual limit is much lower and starts with 30 km.
Even the current best Surface-to-Air Missiles have a height limit of approximately 25 km. Normal combat planes cannot climb for a horizontal speed higher than 20 km. While planes can take a "running jump" by going full throttle upward (e.g. the F-15 up to 30km), they cannot target well and it gets worse with every km going up.
Some powers have the MiG-25, but those planes will be of limited value against targets over 25 km (this includes the SR-71 which is a spy plane and without weaponry). Superpowers may have advanced satellite weapons available, but they need too much preparation, are extremely pricy and are too valuable to send against a target because it tells the others much too much about the capabilities of a nation.
So if you climb up with a stratopheric balloon over 30 km, every nation on earth is practically helpless. I don't need to say that such a stunt would really tick off a nation and is by no means recommendable.

Current antiballistic missile systems have no trouble reaching altitudes higher than 30 km. Proliferation of those is limited, but increasing.

@Hobbes It may be counterintuitive, but ABMs are unusable for the task of intercepting a weather balloon over a nation. The task of an ABM is to intercept very fast moving targets which are still far, far away during the start phase (thousands of kms). This means during the start ABMs are giving everything to increase velocity as fast as possible and they are moving out of the atmosphere because this is the only way to gain enough speed. So they are rising extremely fast and during this phase their control system cannot adjust their course enough to hit a target only hundreds of kms away.

somewhat related: What kind of drone might be able to fly so high that it “operate(s) outside national boundaries”?

There must be a altitude or height limit between national and international airspace.

I think your premise is false.
So far as I know, International airspace is always defined by lateral extent, not vertically.

Travelling vertically from a nation's territory you pass from national airspace into space without passing through anything internationally recognised as international airspace.
The FAI, IOP and others use the Kármán line with reference to the limit beyond which orbital forces predominate over aerodynamic forces.

There's clearly some understanding there's a vertical limit, even if it's not concretely defined, or the US and Soviets/Russians would've been yelling at each other over airspace violations since the 1960s.

@ceejayoz: Space lacks¹ air and is therefore not airspace. US satellites did/do not pass through Soviet/Russian airspace and vice versa. (¹ to any significant extent - less than required to support an aircraft)

If there's not a defined international standard for the minimum molecules of air per square meter, that distinction is really pretty meaningless.

@ceejayoz, the point is, travelling vertically from a nation's territory you pass from national airspace into space without passing through anything internationally recognised as international airspace. The FAI, IOP and others use the Kármán line with reference to the limit beyond which orbital forces predominate over aerodynamic forces.

No, there is no defined height limit to national airspace, but there is an upper speed limit to national airspace, or should we say, an interlock between speed and altitude.
Any aircraft that must generate net downlift in order to not gain altitude can be safely to be orbiting rather than flying.
And for all practical purposes, all orbital flight is considered to take place in international airspace (or in cases where the altitude is so high that the atmosphere is truly neglible, you may prefer to call it international spacespace.)
The higher the altitude and thus the further from the earth's gravitational center, the lower the speed required for a body to be considered to be orbiting rather than flying, and thus safely beyond the limits of any national airspace.

What about suborbital flights (e.g. early rockets reached higher altitudes than LEO while not reaching orbital velocity)?


text:
Is there a maximal time to pass a type rating?
Let's say you begin a type rating for a long haul carrier (e.g. A350 or B787) at day 1. After few days, your training stops due to external causes (airline paying your training bankrupt, all aircraft are grounded in your area due to Eyjafjöll ashes, or even in a larger area due to a pandemic such a covid19,...).
Is there a time limit to resume your training? If so, what is the maximal allowed time between the first day of your type rating training and the day you pass it?
This question can be restricted to A350 and B787 under FAA and EASA regulations if needed.

Nope.  Not unless your employer refuses to continue training.  Legally all that’s required is that you have accomplished all the training required to meet the prerequisites per §61.39 and meet the practical test requirements per §61.43 plus meet the eligibility requirements for the grade of pilot certificate you are applying for per §61.103, §61.123, or §61.153.

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sort: votes


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How can a two-engine B787 create three contrails?
Today I noticed overflying aircraft (over Sydney at FL400) which appeared to have three contrails. When I checked Flightradar24 app, I saw that this overflying aircraft is B787.
What would be the reason for three contrails with only two engines? Could the third be caused by APU, or just by a wake turbulence, or anything else?
I tried to take a photo using binoculars (sorry for the quality, I tried my best). And also a screenshot of the A/C from Flightradar24 app.

Clearly it's the auxiliary chemtrail engine :P

I'm giving you a +1 just for the cell-phone pic through binoculars effort! Nice to know that works out pretty well!

Related.

Just FYI, although the "wave interference" explanations here are likely correct, there are such things as "aerodynamic contrails". These don't originate in engine exhaust, but rather due to rapid compression and expansion of air as it's disturbed by the rapid passage of some part of the aircraft. Almost every day if you're under the approach at SAN you can see these in wingtip vortices. No engines there. On one landing when I happened to be behind the wing I saw a contrail coming off of one of the hydraulic actuator fairings.

Looks like a diffraction pattern to me.

Contrails are created due to variances in the pressure of the air, coupled with the amount of moisture in that air.  When the 2 engines of the B787 blast their exhaust out, the high pressure of the exhaust temporarily causes the moisture to condense.  Two contrails are visible.
However, as the pressure waves from the 2 exhaust trails propagate through the open atmosphere, they interfere with each other.  This interference can also affect the pressure of the moist air between the 2 "primary" contrails, sometimes resulting in another, "secondary" contrail.  In fact, because of this, if there were enough moisture in the air, and the engines were powerful enough, there wouldn't actually be just 3 contrails.  Rather, the contrails would present themselves as the crests of a propagating wave much like the crests of water waves as a duck swims by.  In effect, we would see the 3 contrails separating, and between each of the 3 contrails, 2 more "tertiary" contrails would be visible.
Here on Earth though, the pressure variances and the density/moisture content of the air normalize far before any of that exotic pressure wave stuff could occur.  Except we DO get that one in the middle!

It's not condensation but freezing what causes contrails. And much of it is caused by tiny particles (like soot) and not pressure fluctuations.

@Peter -- yes, that's true. However, the rest of what he wrote is still correct (the part about interference patterns) and applies independent of the cause of the trail's formation.

To say that I am skeptical is an understatement, even putting aside having flown alongside contrails and seen that they are nothing like interference fringes, but let's start with one straightforward issue: this theory depends on the engines being coherent acoustical sources, which they are not.

@sdenham -- The theory depends on the engine exhaust creating spatially coherent concentration gradients (which they do). https://i.sstatic.net/IGnc9.png

@DrFriedParts That is a completely different claim, with 'spatially coherent' gratuitously added to make it look relevant. Tim's answer specifically claims the effect is due to interference between pressure waves, and interference between waves is a specific phenomenon of physics that is not relevant here.  In general usage, 'interference' may loosely mean something like 'interaction', and the interaction of the two vortices may well be the cause of this phenomenon, but that overlapping usage does not in the slightest justify attributing this phenomenon to the interference of pressure waves.

@sdenham -- The interaction of the two vortices is precisely a field interference pattern. It's the same pattern you get with EM field interactions, pressure interactions, etc... My comment was that you were right about the domain being wrong, but Tim's reference to the interference pattern is still correct as it's the same phasor math. Whether it's density or pressure, the pattern you're seeing is a phasor field interference pattern.

@DrFriedParts I get the impression that you are scouring the web for terms that make it look like this answer might, in some technical sense, be correct. Your use of the term phasor immediately brings us back to my original point, the non-coherence of the sources, which you have so far avoided addressing.

@sdenham Coherence requires that for some function f(t+p) and another function g(t+q) the difference can be described by a function h(f+c). That's clearly the case as you can see from the images. If the functions are spatial describing how the concentration is distributed (let's simplify to 1 dimension for now) scan across the image (1 line) and model the color/concentration as y and the linear position as t you get a coherent result. The interactions of the two contrail patterns generated produces a constant result for constant input -- e.g. the sources are coherent.

@sdenham Not trying to be offensive. Seems like you know a lot about the domain. I was just pointing out that everything you said was right except, "interference between waves is a specific phenomenon of physics that is not relevant here" -- which isn't true unfortunately.

@DrFriedParts My original post addressed Tim's claim that this phenomenon is due to the interference of pressure waves. You doubled down on this when you introduced 'phasor' into your pseudo-explanation - a concept that is mysteriously missing from your latest attempt to hand-wave the issue away. In the context you and Tim have established, 'coherence' has a specific meaning that you have still not addressed. You are still trying the fallacy of substituting an alternative (and vague) meaning for a word regardless of whether it is a valid substitution that makes sense in the specific context.

@sdenham -- I'm not sure why you can't understand the difference between wave and pressure wave, but because you can't, you continue to defend the incorrect conclusion that wave interactions aren't in play. I did not "double down" on pressure waves. I pointed out that you threw out the baby (wrong domain) with the bathwater (correct physical model). I tried to explain why contrails are coherent in other domains simply for you, but it seems like you don't have enough experience with wave/field theory (like the definitions of phasor, coherence, et al.) to follow.

@DrFriedParts There is a domain error here, but it is yours. Tim's answer claims the phenomenon is due to the interference of pressure waves, and in that domain, the relevant issue of coherence is this one - note the second sentence: "Coherence is an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference."  Earlier, you wrote "Tim's reference to the interference pattern is still correct", but when faced with its problems, you try to redefine coherence as any scalar sum, which is nonsense.

@DrFriedParts I could go on, but I think the only way you can salvage something from this hand-waving mess is to post your own answer, in which you show how "the pattern you're seeing is a phasor field interference pattern", like "EM field interactions, pressure interactions, etc.", complete with the "phasor math" that justifies your claim that "Tim's reference to the interference pattern is still correct", in sufficient detail that your claims are unambiguous and fully explained. In particular, don't worry that we won't be able to follow if you do the topic justice - you might be surprised.

Fascinating question. Not being an expert in contrail aerodynamics I'm forced to speculate, but I'm guessing the apparent three trails is caused by the spreading of the trails by wingtip vortexes.
I find similar examples called hybrid contrails. Here's one animation of a four-engine A340 from that article:

I think if you ignore the trails from the outer engines, this looks similar to your photograph. Here, the inner trails are twisted and spread by the wingtip vortexes into a pair of semi-transparent "tubes" of condensation trailing the aircraft. The apparent darkness of the tubes is thickest at the edges, since at these points we are looking through a greater thickness of vapor. As the tubes expand they touch, leaving three areas at the red arrows where the trail appears darkest from below.

A similar formation can be seen in the first few seconds of this video. It happens quickly, but paused at the right moment there appear to be three trails:

Within the next second the formation has spread enough it becomes an indistinguishable single trail again, but under conditions less favorable for persistent trails such as in your photograph, the trail may have dissipated by this time.

Those three contrails that formed are diverging, while maintaining some coherence. It's hard to be sure, but the third one seems to appear when the diverging fan of the initial two reach the centre line of the airliner. My guess is that they mark the vortices (vortexes) in the air shed by the tips of the flight surfaces. There's a big one coming off the end of each wing, and a smaller one coming off the end of each horizontal stabilizer. These latter are too close together and probably too much generally affected by turbulence generated by the fuselage to be seen as distinct.
So initally, two: one source of ice crystals emerging from each engine. But these then get sucked into the vortices, and two transitions to what appears to be three.
The trailing vortices of a big airliner are huge. They can cause serious turbulence for another airliner crossing the "wake" of a previous flight, and can cause damage or loss of control for a small aircraft. They are one of the good reasons for a mandatory minimum  separation between aircraft approaching an airport.  (ISTR, three miles).

I expect the earlier explanations are correct, but it also strikes me that there are more that two jet type engines on a 787 - the APU is right there in the middle and while its exhaust isn't nearly as strong as the main engines I can imagine that it might be strong enough to perturb the flow at the point where the main jet exhaust meets and have a visible effect on the main engine exhaust flow.

Nope. There are restrictions on the operation of the APU. Varies by brand, but it may not light-up above 15'000 ft, operation above 25'000 ft is not allowed, or operations are not recommended. No major airline has a standard operating procedure that includes APU use on cruise.

There certainly are APUs capable of starting/running at all altitudes.  I believe this is an ETOPS requirement, or ETOPS has other requirements which have that same effect.  I expect the reason is at least some planes need the APU to cover some ETOPS contingencies -- descending to 15,000 is out of the question as it would worsen their fuel economy so they could not meet their ETOPS range requirements.

@DrFriedParts: Is that a worldwide restriction? Or specific to your personal country of origin?

@LightnessRacesinOrbit DrFriedParts seems to be saying that it's basically part of the APU "owner's manual", not a legal restriction.

@DavidRicherby: Oh yes, the "varies by brand" does suggest that, thanks.

@Harper -- ETOPS APU's are required to be able to start in flight reliably from cold-soak or remain on the entire flight (no manufacturer/operator chose this latter option for obvious reasons). However, my original statement is still correct. No major carrier suggests using it on cruise (except in certain emergency scenarios) and many models of APU deployed today do not run above 25k'ft. So either it can't or you shouldn't.

@DrFriedParts For some reason, I don't know why, I was thinking in the context of the 787 Dreamliner.  Of course your statement is correct for some aircraft.  My bad... I wonder why on earth I was fixated on the 787.  shrug...

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Is there a taxi turning radius requirement for normal category aircraft?
Does anyone know if there is any requirement regarding turning radius during taxi for a normal category aircraft?
I searched both the Part 23 and Part 91 from cover to cover and couldn't find any. If there is no legal requirement but a recommendation from some Advisory Circular or any other document I also would like to know.

There is no legal requirement. In fact there is no stipulation that the aircraft be maneuverable on the ground.
Good examples of this are early aircraft (often biplanes) with tail skids. In the middle part of the last century there where gliders that had no wheels - just a center skid. Many current gliders have just one wheel and it is not steerable.
"The nose gear of a few aircraft with tricycle-type landing
gear is not controllable." FAA Airframe Handbook pg 13-4
These type of aircraft are usually steered using differential braking. Examples are: Grumman (AA1, AA5, AG5), Diamond (DA1, DA4), Rallye except the 235C, early "straight 35" Bonanza, Columbias, T-28, T-34C, Nanchang CJ-6A, HU-16 Albatross, IAR 823, etc.

The HU-16 Albatross does not have steerable gear

Aircraft without wheels

Glider without steerable gear

You will find some information on assumed turn radii in the ICAO Doc 9157 - Aerodrome Design Manual Part 2. For the purpose of taxiway design, they assume a relation between taxispeed and turn radius according to the following equation:
\begin{equation}
V^{2} = 127.133 * (f) * R
\end{equation}
with radius R given in meters, lateral acceleration assumed to be limited to 0.133 g and velocity V measured in km/h

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What is the difference between a tail slide and a whip stall?
Can someone tell me what the difference is between a tail slide and a whip stall?
Whip stalls are prohibited as far as I know in the C152 Aerobat but watching a video of a whip stall it looks exactly the same as a tail slide. The thing is that my aerobatic instructor taught me how to tail slide and I distinctly remember him telling me to make sure that I held the elevator neutral or it could snap off or be damaged.

According to this answer, What is a whip stall?, you're right - they're the same thing.

A "tail slide" occurs when an aircraft is nose up and loses all forward airspeed. Gravity then pulls the plane "backwards" towards earth.  The "whip" occurs when a sinking aircraft is flipped nose down by the airflow as it assumes a more aerodynamicly stable orientation.
Aircraft will generally nose down when they sink due to more area behind the center of gravity than ahead (as viewed from underneath the plane).  The horizontal stabilizer, farthest from the CG, is the main contributer, especially with down el.
Note that with canard and delta designs, it is the back of the main wing serving this function.
The issue is that when one tail slides, the increased vertical sink rate turns a gentle nose down into a hard "whip", greatly increasing stresses on the aircraft.  There for it is imperative to make sure the plane can handle this and not to tail slide too long.
For hang gliders and "flying lawn chair" type aircraft, a hard whip can be induced by pulling forward too aggressively in stall recovery (deltas have big tails), resulting in a full blown forward tumble.
Definitely something to discuss with your acrobatics instructor.

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Which radio frequency is used during a flight interception?
What kind of communication do the intercepting and intercepted aircraft use? Is it the usual air-to-air frequency or the international emergency frequency?

I think you might need to expand this a little bit. What sort of interception are you talking about? In what jurisdiction? And why do you think this is specific to VFR?

An interception with an aircraft that's either on an unknown frequency, or non-responsive etc will be conducted on the emergency frequency of 121.5. Likewise, a pilot would be expected to tune into that frequency if they found themselves the subject of an interception.
There is no other standard "air to air" frequency that's likely to be utilised. I'm aware that some countries have special frequencies reserved for formation flight etc, but most pilots wouldn't have those memorised and wouldn't be expected to use them.
However, if the aircraft is/was communicating on a known frequency then there'd be no reason that an interceptor couldn't use that.


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What is the difference between variable and transient bleed valves?
What is the difference between variable bleed valves (VBVs) and transient bleed valves (TBVs)? What is their range of operations? Can they be used at all airspeeds?

Welcome to aviation.SE! Have you already seen this question on transient bleed valves?

Turbofan engines have two or three distinct spools made of some turbine stages driving compressor stages using a shaft. The turbine stages collect the energy from the fuel combustion hot gases and drive the compressor stages which feed the combustion chamber with air.
When the fuel rate changes due to throttle position being changed, a delay is needed for this spool system to adapt, the time their rotational speeds adjust for a new equilibrium. However a turbine engine compressor is a tricky system in which the compressor must never stop producing air for the fuel combustion, and indeed must never allow hot gases from the combustion chamber to return forward, else the air pump is drained, the turbine stops producing power to turn the compressor, and the compressor itself stops compressing air.
The role of the VBV and TBV, as well as other elements (variable stator vanes, active turbine blade clearance system...) is to maintain the engine in conditions which prevent it to stop. The position of all these mechanisms is determined by the engine controller, which today is electronic and digital, and comprised of the FADEC, the EEC/ECU and the HMU.
While the VBV deal with more general equilibrium, the TBV deals which very quick transient states found in engine accelerations. In both cases the device reroutes a given quantity of air in the core to another location.

Source
Shared characteristics:
On a CFM56, the Variable Bleed Valves (VBV) and the Transient Bleed Valve (TBV):

Are both part of the engine control.
Are actuated by the HMU under the control of the ECU (EEC).
Are used to maintain the compressor pressure within the optimal compression region when the rotational speed of the compressors (low and hight pressure spools) changes and a new equilibrium between spool speeds needs to be achieved.
Prevent stall.

The VBV:

12 VBV located between the booster and the HPC (within the fan frame).
One or two "master valves" which drive the other.
Reduce water and foreign object ingestion.
Open when the engine decelerates or at low speed.
Close when the engine accelerates or at high speed.
When open, air from the hot flow is discharged in the bypass flow.

Source

Source
TBV:

Single valve located between the HPC stage 9 (bleed air tap) and the LPT stage 1.
Is aimed to quickly react after transient HPC pressure changes.
Improve HPC stall margin during engine start and acceleration.
When open, air from the HPC is discharged in the cavity before the LP turbine.

Source

CFM56-7B, Source
More on this site:

What is the transient bleed valve in a gas turbine engine?
Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow?
How does the FADEC prevent compressor stall during rapidly increasing thrust demand?

On a CFM56, the transient bleed valve (TBV) system controls the quantity of the high pressure compressor (HPC) 9th stage bleed air that goes into the stage 1 low pressure turbine (LPT) nozzles.
The TBV system increases the HPC stall margin during engine start and during engine acceleration.
The variable bleed valve (VBV) system lets a part of the low pressure compressor (LPC) discharge air go to the secondary airflow.
During a fast deceleration, the VBV system prevents an LPC stall.
At low engine speed and during the thrust reverser operation, the VBV system keeps unwanted materials (such as water or gravel) out of the high pressure compressor (HPC). This prevents damage to the engine and improves engine stability.


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Is there a limit to the possible altitude for electric jets?
So I was thinking about Elon Musk's supersonic electric jet idea. Assuming we have sufficiently energy-dense batteries, where would the limits be in terms of speed and altitude.
His logic seems to be: electric (fan?) propulsion doesn't need oxygen -> can go higher -> less friction -> need less power and thrust to maintain airspeed compared to traditional jet
Question: is there some kind of limit for altitude and TAS? I mean suppose the Concorde would be retrofitted with batteries and electric fans. Instead of mach 2 cruising at 18300 meters, assume it would climb to 30km, or even 40km. Air density at 18.3km is 0.115 kg / m^3, at 30km it's 0.018 kg / m^3 and at 40km it is 0.0039 kg / m^3.
So 0.0039 / 0.115  = 3.4%. Meaning the resistance at 40km would only be 3.4% compared to 18.3km. Would that mean the power or thrust requirement to maintain mach 2 would only be 3.4%? Or is induced drag becoming significant at that point? Or maybe it would even stall at mach 2 if flying 40km high?
I mean somehow there must be limits, otherwise we could just fly higher and higher and fly with 0 thrust and still maintain mach 2 (not talking about space flight here)?

Well, you need lift as well, which also reduces with increasing altitude.

Well, lift is dependent on dynamic pressure to the same degree as drag, so, theoretically, at almost any altitude, as you increase speed to that same dynamic pressure that would produce the drag you have the power (thrust) to overcome, you would have the same amount of Lift, no?

Another consideration is that as you go higher, and faster, Lift required decreases due to centrifugal force. Obviously, just outside the atmosphere, 200 miles up, orbital velocity is about 18,000 mph. So airspeeds at some significant percentage of that will garner the benefits of some reduction in required Lift. (to a degree dependent on speed and what direction you travel - with or against the eastward rotation of the earth)

If you remove the limitation of battery the next limitation is probably weight. At high speed and high altitude the engine would probably a jet with high exhaust velocity, where hot jet (e.g. turbo jet, ram jet, and low-bypass turbo fan) has a clear weight advantage over cold jet (e.g electric jet). IMO if you want low carbon super sonic travel implemented with reasonable amount of time and money budget, hyperloop would be slightly more practical, or hydrogen fuel.

Isn't the real limitation the amount of thrust you can generate from a fan or propellor?  Which is going to depend on the density of the medium: consider the size difference between airplane & boat propellors generating the same thrust.

That electric propulsion needs no oxygen is of little help for flying high. The composition of the atmosphere does not change too much with altitude, so it is the low atmospheric density which limits maximum altitude. We had this discussion before, and indeed solar-electric propulsion helped to reach record altitudes: The AeroVironment Helios set a record at 29,524 m which will be hard to break.
Supersonic speed helps to fly high - while subsonic designs run into the coffin corner, supersonic flight helps to maintain high dynamic pressure even at altitude. However, the energy requirements for doing so will require an energy density of the batteries which is several magnitudes above what is currently possible. If you only want to go fast, the current limit with electrical propulsion and already rather generous assumptions is somewhere around Mach 2.
Flying higher does not reduce the thrust requirement since the same lift has to be generated. The best lift to drag ratio is achieved in subsonic flight. Going supersonic means crossing a drag peak, but beyond that the maximum possible lift to drag ratio is well below that at subsonic speed and decreases again with increasing Mach number.
Mr. Musk is clearly out of his competence when he claims that supersonic electric airplanes are viable, even with the progress in battery technology to be expected in the next few decades.

I looked it up a bit and the available info seems very vague. The main idea seems to be that it is VTOL. I am guessing that even when supersonic it gets lift mainly by vectored thrust. And that it is more of a "potentially supersonic due to high engine power and low drag" than "actually has the range for supersonic to make sense". I guess "supersonic" is mostly because it sounds cool? It seems rather incidental to the main concept anyway.

@VilleNiemi: Electric VTOL is even more challenging - the only remotely realistic concept I know of is from Volocopter, and there are quite a few out there.

Yeah, but all the articles were specific about VTOL. I don't think its possible unless the intended range is short. Which would make supersonic performance irrelevant.

I guess what I have trouble wrapping my head around is the following: let's say in a Cessna 150 I cruise at 100 knots IAS at sea level (ISA). Then the TAS would be also 100 knots. But when I climb, and IAS stays at 100 knots, the TAS would more and more increase because the air is less dense and so the plane can fly faster through the air until it meets the same resistance than at SL. So the plane still "thinks" it is flying 100 knots even though it is faster already. Why wouldnt it be the same for a supersonic aircraft like the Concorde? Is it different due to some kind of supersonic effects?

@user15864: In subsonic flight it is indeed as you say (apart from density-related effects like less damping, and temperature-related effects like more friction drag and more heat engine efficiency), but when you come close to the speed of sound a new kind of drag emerges which will spoil the picture.

It's worth recognizing that many of the things that SpaceX and Tesla are doing were also decreed to be impossible or very unlikely several decades ago. That's no guarantee he will succeed at this endeavor, but worth pointing out.

@enderland: McDonnel-Douglas demonstrated re-useable rockets a quarter of a century ago. However, the cosy duopoly for rockets in the US saw no need to advance to an orbital version. By hiring the best engineers from both, SpaceX had no problem to actually build the real thing. With Tesla, Musk happened to buy a company which was serious about doing EVs right, with lots of battery capacity (what their competition avoided). In both, Musk showed good engineering judgement. He does not with aircraft, however.


text:
Can pretty much anyone run/operate a primary radar?
Thinking about increasing the amount of information one receives beyond that from one's own 1090 MHz ADS-B in receiver when following aircraft as a hobby, is it perceivable and possible to operate a low power primary radar? What limits exist on emitting power and what must one be aware of?
In general, it would be interesting to know about this from the technical and legal feasibility perspectives of EU countries such as Germany and France or others like Switzerland.
In this paper, the concept of using a smaller primary radar while airborne is explored without mentioning the regulations/legal requirements to do so.

Welcome to Aviation.SE! Are you asking about technical feasibility or legality? If legality, please add which country you are asking about?

Many people operate primary radar-like devices, they are found commonly on small pleasure boats. However I'm not sure what information radar will give you over ADSB, many airports are ditching primary radar for secondary systems...

Government-operated PSRs operate in the 1.4GHz and 2.7-2.9GHz ranges,which have been set aside for aviation use by the FCC and international bodies. You will have to get licensing approval for your device to operate it in those bands, or use an unlicensed/general-purpose band like 2.4GHz (which will cause problems with your WiFi setup!). 1090 and 978 ADS-B receivers do not have this problem because they are RX-only, snooping on information the planes are broadcasting already.

@randomhead No way you can legally use the ISM ("WiFi") bands for radar. Any public use of those bands is limited to low power transmission which is incompatible with the entire idea of a primary radar. A radar needs a powerful transmitter and a super-sensitive receiver, because just a minuscule fraction of the transmitted power gets reflected back. Good luck picking up that faint echo in a horribly noisy band.

@TooTea I did say it would cause problems... and I would also say "Good luck getting the regulatory body to approve your home-built device that probably interferes with existing radars because it uses the same band." The point I was making is that frequency bands are a limited resource and the answer to OP's question is likely "no, it is not permissible."

@mins, I'm not sure how that is helpful to OP. Obviously devices using those bands must be properly licensed and certified, as I said, whether they are land-based or airborne.

And @TooTea, you are incorrect about "public use of those bands being limited to low-power transmission" (at least in the US). 14 CFR 18.305(a): "ISM equipment operating on a frequency specified in § 18.301 is permitted unlimited radiated energy in the band specified for that frequency."

@randomhead I was thinking more about WLAN and less about microwave ovens. I don't have the slightest clue how the US regulations tell those apart, but there are radiated power limits for WLAN in 47 CFR 15.247.

This is a radio regulatory question rather than aviation. If this question gets closed as off-topic you may try https://ham.stackexchange.com/ - don't post on both at once as it's considered impolite, but if this question is declared as "not aviation-related" then you may ask there.

In most countries, including the US and in Europe, it is illegal to operate any self-built RF transmitter without a license. That includes the ISM band. ISM transmitters are exempt from the need for an operating license, but building transmitters for this free band is still restricted. The builder or manufacturer needs to certify that the device indeed respects ISM specifications.
Someone with a Radio Amateur license may build and operate RF transmitters under certain restrictions.
The Radio Amateur license might cover radar experiments at least in some countries, see this  question on StackExchange for Amateur Radio: https://ham.stackexchange.com/questions/14650/can-i-use-a-amateur-license-to-experiment-with-radar.
Universities and companies that do research on or development of radar, and need to test radar equipment in the field, require some sort of license for their organization.
In any case, your question seems to be about operating existing radar units, rather than building one yourself. The situation should be somewhat similar for aviation and marine radar. If you buy a (legal) aviation (or marine) radar unit, this device will be certified, and allowed to be operated by a certified user. That user will require a pilot license (for planes, or radio license for boats). The device certification only covers operation in the intended environment, that is built into the plane (or the boat), but does not cover land based operation, away from the plane (or boat). You may find discussions about that in the internet (like https://www.reddit.com/r/amateurradio/comments/7zu3x5/does_anyone_have_experience_operating_a_marine/).


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What are the relative efficiencies of the various stages of a counter rotating propeller?
After going through the CFD results of a drone project I am involved in, I noticed that the data shows significantly increased (+10%) thrust generation at the second stage of a counter-rotating, 2-stage, ducted fan. Both stages use identical airfoils and spin at the same rpm. They also have low solidity, meaning they look more like propellers than airliner fans, as the blades take up a small proportion of the disc area.
Generally, propellers are less efficient when the incoming airflow has a high velocity, so I would expect, in any N-stage fan using otherwise identical stages, for the N stage to produce less thrust than the N-1 stage, but apparently I am missing something.
In a previous answer here Peter Kämpf mentioned that the first stage of the Kuznetsov NK-12 turboprop pre-swirls the flow to improve thrust creation conditions at the second stage. How does this process work? Does it require a specific design of the stages to work in tandem?

The key thing to think about is that the first stage doesn't just accelerate air downwards, it also causes it to rotate ("swirl") in the same direction as the first stage propeller.
This happens because the first stage propeller, being an airfoil, generates both lift and drag. The lift corresponds to air being accelerated down the axis of the duct; the drag corresponds to air being accelerated circularly around it. The amount of swirl force is therefore related to the thrust and the effective L/D ratio of the propeller.
The airfoil of the second stage propeller is then encountering air that is moving towards it at the tangential velocity of the propeller, plus the tangential velocity of the air that has now been circularly accelerated ("pre-swirled") in the opposite direction by the first stage.
That increased velocity means that the angle of attack for the second stage airfoil will be increased compared to that encountered by the first stage, and hence greater lift is produced at the same RPM.
To balance the load on the two stages you would need to adjust the pitch or RPM of the second stage propeller.
Note that after the second stage, the air will be "unswirled" back to being closer to a non-rotating flow, and this is one of the reasons that a contra-rotating pair can be more efficient than a single propeller: overall, the system wastes less power in swirling the air rather than accelerating it axially.

I've wondered about that; if you want to have two counter-rotating propellers like on a drone, that are fixed pitch, it wouldn't do to have the same pitch on both  propellers.  The second propeller should have a bit less pitch then, if it's going to operate at the same RPM as the first one and you want it to make the same thrust?

Thanks for the answer. I understand what you mean to say regarding the induced velocity from the first stage on an intuitive level, but I feel it could be clearer. Also in your second and third paragraph, you use radial to describe the swirl component. Radial is usually used to denote something along the radial vector, I think you meant to use azimuthal or angular.

@JohnK you could give the second propeller less pitch, or you could also just operate it at slightly lower RPM. On a typical electric multirotor, adjusting the RPM would be far easier, since then you could stick to all your propellers being standard types with the same pitch.

@AEhere thanks for the feedback. I've replaced the misuse of 'radial' velocities with 'tangential'. Angular velocity would not be correct - that refers to a rotational velocity in e.g. RPM or radians/second, whereas what matters here is the linear velocity of any given point along the propeller blade, tangential to its circular path.

The aft propeller operates in the higher pressure environment that the front propeller generates. Thrust is a function of the stagnation pressure of the incoming flow - same principle as translational lift in helicopters.


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How does the reverse thrust work while landing?
During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction to counter the aircraft's forward motion if I'm right So, my question here is "does the engine stops its rotation(clockwise) and than starts to rotate it in opposite direction(anti-clockwise) So, as to perform the reverse thrust operation?
In a nutshell my question is does the engine stops midair to perform the reverse thrust operation!

During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction

This is wrong
Reverse thrust does not reverse the rotation of the fan/compressor/turbine.
Reverse thrust "simply" redirect the airflow coming out of the turbine in the reverse direction (well, almost, as we'll see in a moment) w.r.t. the usual one.
In the image you posted, the thrust reversers are deployed, and you can see them circled here:

The airflow is the coming out not from the back of the engine, but from the sides, slightly directed forward. The thrust (i.e. the force that the airflow is imposing on the aircraft) is directed backwards, while normally is directed forwards, it is then reversed.
This is nicely illustrated in this image (source)

NOTE: there are different typologies of thrust reversers, this is only one of them, but none of them require spinning the engine in the opposite direction.

Thankyou for making me right..and it was a good information indeed.

Not illustrated: The fan airflow (deep blue) is much larger than the turbine airflow (red), and as much as 90% of thrust comes from the fan airflow.  Thus, in reverse mode, the "red" continues to be forward thrust, but there's not enough of it to make a difference. The red is more turbine exhaust than intentional thrust on a high-bypass. The fan does "all" the work.

When you put your car in reverse gear, does the engine first stop and then start spinning in the opposite direction? No. The engine still keeps on spinning in the same direction, it's some extra gears that cause the output to be in the other direction
Similarly, Reverse thrust is merely a deflection of thrust from the rear to the front. It is done using mechanical levers and gates that redirect the flow of thrust to the opposite direction.
If reversal of turbine's rotation was hypothetically required, the resultant reverse thrust would be produced too late and negligible to be of any use. You can't stop a turbine from a massive RPM to nothing within a few seconds, and then spool it up again in the other direction.

Turbine working in opposite direction won't work at all. Shapes of all rotor and stator blades are optimised for so-called forward airflow, temperature gradients and pressure gradients at every stage. The least bad thing that can happen when you try to reverse the rotation is complete stall of the turbine stages. Similarly, inversing the crank rotation of 4 stroke engine will produce no power output at all. On the other hand, 2 stroke engines can run both directions.


text:
Can an aircraft engine be started midair?
Can one start the aircraft's(commercial/fighters) engine midair at high altitudes especially turbojet or turbofan engines?

Related


text:
What is that decommissioned plane near Nadirgul Airfield?
This is a decommissioned plane that I found at my place. I'm guessing it is a Dakota DC-47.
The plane is placed near a small airstrip called Nadirgul (name of the location), which lies in the outskirts of the city Hyderabad, India

This is right, this model is a C-47A-85-DL Skytrain, a variant of the "Dak" DC-3 selected by the US Army Air Force in 1941 as its standard transport aircraft.

Image from Le Bourget Air & Space Museum
It has been early used by Allied forces to drop paratroopers and equipment or to tow gliders behind the coastline for the D-Day and operation Overlord.

C47 from 439th Troop Carrier Group and Waco with their invasion stripes taking off from England for Utah Beach, June 1944 (source)
It had a long history and was everywhere until the end of the war and in the post-war conflicts, e.g. many of them participated to the Berlin Airlift:

C47s unloading at Templehof airport in Berlin, 1948. Source
Differences with the DC-3 include:

cargo door
hoist attachment
strengthened floor
shortened tail cone for glider-towing shackles
astrodome in the cabin roof.

You said the aircraft was standing at Nadargul airstrip. This information has been very useful to find the exact aircraft. It happens the aircraft did have a long story, throughout eras of war and peace, linking people of many countries:

A C-47A-85-DL airframe with c/n 20012, is manufactured in Long Beach, California, by Douglas (source) for the USAF (registration 43-15546).
In 1946, right after the war, it becomes the French government property (F-BAXK) operated for cargo flights under Air France colors.
Sold in 1950 to Portuguese government to be operated from Lisbon by Aéro Portuguesa (CS-ADB).
1953: Leaving Europe when sold to Lebanon, operated by Air Liban (OD-ABQ).
Finally moving further eastwards to India, bought by Kasturi and Sons (VT-DTS) to deliver The Indu newspaper in distant areas until it is decommissioned and transferred to Nadargul where it is used now by the Flytech Aviation Academy for ground training (source).

(Source)
A movie star
This aircraft is seen in the 1965 Hindi feature film, Gumnaam (video):

Stamps in Israel
The aircraft was used for the first aerial mail sacks sent in 1948 from Israel to European countries, when it belonged to Air France. Two stamps commemorated in 2008 "60 Years of Friendship between Israel and France":

On June 9, 1948 an Air France DC3 airplane, registration number
  F-BAXK, landed Haifa, flown by pilot Georges Bernard and two crew
  members: communication technician Mr. Sortais and mechanic Mr. Boutet.
  The plane made an interim stop in Bucharest while en route to Israel,
  thus arriving with mail from both France and Romania. The plane
  subsequently left Haifa on June 11 at 6:36 a.m., bearing mail to
  France and other countries with which Israel had re-established postal
  ties: Bulgaria, Holland, Hungary, Yugoslavia, Poland and Switzerland.
  It also carried a mail sack bound for New York. After interim stop in
  Cyprus, Greece Italy and Nice in southern France, the airplane took of
  the next day towards its final destination, Le Bourget airport in
  Paris, where it landed on June 12, 1948 at 11:01 a.m. and delivered its
  mail sacks.

(Source)

That's plenty of information..... thankyou for your dedicated curiosity and exploration..... great work...!

Fantastic legwork, compiling this answer! Thank you.

It is either a Douglas DC-2 or DC-3.
The difference between the two is the length and the wingspan: The DC-2 has a length of 19,1 meters (62,7 ft) and a wingspan of 25,9 meters (98,1 ft) and the DC-3 had an length of 19,7 meters (64,3 ft) and a wingspan of 30,0 meters (98,4 ft)
Since I can't really see the full length of the aircraft in your picture, if you roughly know the wingspan, you can identify the aircraft.
But if you really want to know which version it is (e.g C52, D-42) you should take a look on the wiki pages (DC-2) (DC-3)

It's a DC3. The DC2 had landing lights in the nose cone.

@tj1000 it's hard to see on a picture this resolution, but I see some kind of light cone on the nose.

@HugoWoesthuis the DC2 has very pronounced protrusions on the underside of the nose for the lights which are missing in this aircraft. It also has a quite different shaped vertical stab (which is not visible of course in the photo). Unless it's some custom conversion of a DC2 using a DC3 nose cone, it's a DC3.


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What is this aircraft and its submarine?

I got this picture from an anonymous source and I'm curious to learn more about its mission and I want to know if it's a genuine picture. It happens to be a submarine aircraft carrier.

The Japanese, during WWII, actually built three examples of a sub that could launch and recover a float version of one of their fighter-bombers.  One saw actual service, but was scuttled off South America when Japan surrendered.

yes it was I-400 class submarine.


text:
What sensors are required to fly RNAV 5 airways?

In the example shown above:

Is an aircraft required to have all 3 sensors listed or just one of them to fly the L512 airway? What ICAO reference confirms the answer?
Does 'critical DME' (bottom row) mean an aircraft is required to have DME/DME? Or can an aircraft equipped with GNSS still fly the L512 even when KAE or KPO is out of service?


text:
What's the difference between "HAND OFF" and "HAND OVER"?
I think "HAND OVER" is a whole process of transfering radar idenrification between 2 controllers, and "HAND OFF" is a term used by the transfering controller(not receiving controller) when doing HAND OVER.
Am I right?


text:
Where on the aircraft are transponders mounted?
For civil acft like B737-800 or B777-200, where is the location of transponder?
I'm asking about the "responder", not the cockpit device.

For civil acft like B737-800 or B777-200, where is the location of transponder?

Electronic equipment is distributed at several locations known as electrical compartments, avionics bays, or other similar names, where elements are interconnected and cooled. The different pieces of equipment (line replaceable units / LRU in engineering parlance) are then connected to the cockpit, or to other locations, using the avionics network.
LRU are placed in standard racks. In general these compartments can only be accessed while on the ground through a door at the bottom of the fuselage.
On the B737 NG (-600/-700/-800/-900) there are several racks at the level of the cargo bays, a bit aft of the nose wheel gear:

Source: B737 NG, General Familiarization Manual.
Boeing uses ATC to refer to the transponder. There are two ATC electronic units, both in rack E1. Layout of rack E1:

Source: B737 NG, General Familiarization Manual.
Rack E1 on a B737-800 (without the top shelf):

Source: Airliners.net, photo by Petr Volek
A transponder looks like this (Collins TPR-901):

Source: Collins Aerospace.
There are two connectors on the back panel for the top and bottom antennas (ATC antennas location), and two connectors for the network. This model can be seen on this other avionics bay, for a B737-700 (sorry for the terrible quality):

Source: digi.no.

More: How are electronic systems locked and connected in the electronic bay?
Youtube:

B737 Electrical Equipment Bay
B787: A tour through the brain of the airplane

Suggest adding the location of the transponder antennae. Usually on the bottom of the aircraft?

@Terry: Good suggestion, thanks. I added a link to an existing answer.


text:
Are there any Part 135 (On-Demand Passenger Charter) companies out there that use Aviation Bio-Fuel?
I was recently approached by a client asking if I can provide charters on environmentally conscious aircraft that run on Aviation Bio-Fuel.
Anyone have any insight on what is required for an aircraft to run on bio-fuel?
Who is implementing the use of Aviation Bio-Fuel in their fleet?
How do I find out which airports actually have Bio-Fueling capabilities?

I'm not sure biofuel is even available in larger quantities, it would have to be ordered probably weeks or months in advance, and I hope your clients are ok with paying way more than traditional charter costs. Nobody has implemented it yet, although some have done test flights, and it was approved in 2011.

Biofuel has already been considered and tested on some aircrafts. Here you can find an article about tests.It states at least six of them

At least six airlines, including KLM, Lufthansa and Finnair, have now
  used biofuel on flights carrying passengers.

However there is still a long way to go.On wikipedia it says

The sustainable aviation fuels certification and production pace seems
  insufficient to meet the IATA target of halving the CO2 emissions by
  2050

But airports do not supply bio-fuels for now since you need tons, even for one flight.
And for the list that used biofuel on their commercial flight you can check this list out. On that list i know KLM, interjet,Hainan offers charter flight. So it is safe to say those companies environmentally conscious, if you want.


text:
Can the A380 ferry an extra engine, like the 747?
A useful little quirk about the 747 is that it can ferry a fifth engine on the wing, for when another aircraft is stranded somewhere in the world.

Does the A380 have the same capability? If not, how would an airline manage an aircraft needing a new engine whilst away from a maintenance base?

Two documents mention ferrying (on 3 engines: 3EFF): type certificate and Operational Suitability Data (OSD) for the Airbus A380 Family - A380-800, so I guess it's allowed. No info on ferrying with 4 engines.

@mins, ferrying an airplane with one engine inoperative and ferrying a fifth engine on an airplane are two rather different things (and ferrying might not be the appropriate search term for the later).

Funny that we have these other questions that are related, but not the same
How do you repair a grounded aircraft at a remote location?
How are off-wing jet engines transported?
What are the requirements of ferrying a spare engine?

To be more specific about the special conditions that apply when ferrying an engine on the A380, see requirements "G-06 SC: Ferrying one engine unserviceable" page 297 of Explanatory Note to TCDS EASA.A.110–Airbus 380. Those conditions were the base for delivering the type certificate.

I just saw in the news that a Quatas B747 with Registration VH-OHS just did an engine ferry for another 747 today. http://www.qantasnewsroom.com.au/roo-tales/that-time-when-we-strapped-an-extra-engine-on-to-a-jumbo/

Is the fifth engine place holder only on one wing? Is it not logical to provide slots on both wings for better stability?

it's only on one wing. There is very rarely a need to ferry one engine, let alone two, so no need for a placeholder on the other wing. Not all 747-400s can ferry an engine, it's an optional extra that must be selected when ordering the aircraft - and Qantas is the only airline to have asked for this ability to be fitted. (I believe all 747-100/200/300s had the ability though).  This is the first time they have ferried an engine for 5 years.

Information (maybe) only: A friend recently commented on a QANTAS 747 Ferry flight with an extra engine. He said he knew a passenger on the flight which said it was much slower than usual and they added an extra stop (at Perth). It was from West side of Australia to Africa and then ???.He said it took 12 hours - how long usually I know not but apparently 12 hours was beyond exceptional. .

@RussellMcMahon: Not surprising, given how much drag a non-functioning engine creates.

One of the main reasons the 747 was given the ability to ferry an engine was due to the lack of large cargo aircraft available at the time.
Don't forget the 747 was a major game changer when it came out, it was designed to replace the 707/DC-8, and was almost twice the size of these aircraft. As a result, there just wasn't anything available to transport a 747 engine by air if needed.
This was a major problem that had the potential to affect sales of the aircraft, and so they had to find a solution to this. It wasn't until the 747 began to be introduced as a cargo carrier that it was possible to transport these engines by air, in the hold of an aircraft.
With the introduction of the A380, there was no need to add engine ferry capabilities, as large cargo aircraft were common enough to transport them.

Manager: We need the ability to move engines not in use. Engineer: How do we carry the engines that are in use? Manager: On the wing. Engineer: put it on the wing then. Manager: ¯\(ツ)/¯

The A380 does not appear to have the capability to transport an extra engine under the wing. Higher engine reliability combined with widespread availability of air cargo transport makes this option redundant in modern jets.
In case engines are needed for an A380, they can be transported in a 747-400 Freighter* or the aircraft can be flown with three engines.
*Trent 900 can be transported in a 747-400F without disassembling. For Engine Alliance GP7000, you'll need an An-124.

I'd disagree with the "The aircraft can be flown with three engines" which suggests the flight would be conducted with a failed engine. That wouldn't happen: your source describes an engine failure in flight, which is a very different scenario to your suggestion that it would take off with an inoperative engine.

@JonStory A380 can takeoff with three engines- see mins comment above in the question.

It's physically possible, sure, and I didn't disagree with that.... but it's not acceptable procedure. It can take off on 3 engines if one fails after V1. That doesn't mean an A380 would ever deliberately take off on 3 engines in normal use. The pilot who did that, wouldn't be a pilot for very long. The A380 is designed to take off with one engine out for safety reasons if the engine fails during takeoff: but if you try to take off on 3 engines, you no longer have that safety margin if another engine fails. An A380 would never attempt a takeoff knowing one engine was inoperative.

The article about the An-124 states that bigger engines can be transported in smaller cargo aircraft if partially disassembled.  Since there are only about two dozen AN-124's in commercial service, how long does getting one scheduled for a special flight compare with the time needed to de/reassemble an engine that was sent via a regularly scheduled freight flight?

@JonStory I'm not sure about the A380, but I do seem to recall Terry stating that there were approved procedures on the 747 for repositioning flights with one engine inop. I would assume that said procedures involved an empty aircraft with much lower than normal takeoff weights. Remember that the normal single engine failure on takeoff requirements are assuming MTOW.

Hence why I said normal service. There may well be a maximum weight for which a 747 or A380 can operate win 3 engines (or rather, 2) but I highly doubt that would ever be done in revenue generating service

@JonStory Oh, yeah, agreed on that. Sorry, I missed the "normal use" part there. I assumed that the answer was referring to flying the aircraft on three engines on a non-rev ferry flight for the purposes of getting the 4th engine replaced.

A GP7000 can't be carried on a cargo 747? I'm surprised because according to this data the GP7200 is smaller in diameter than the Trent, although it weighs more; thus, if the issue is diameter, rather than weight, I'm surprised the GP engine won't fit in a 747.

I seem to recall a documentary where they were transporting a GE 90 (777 engine) and they mentioned it was the largest aircraft engine - it was being loaded onto a 777 freighter.

@BurhanKhalid I don't think the 777F can carry the larger variants of the GE90 (the -110 and -115b) fully assembled, but it can carry them with the fan separated from the rest of the engine. Not sure if the 747 freighters can carry one fully assembled or not, but my understanding was that An-124s and such were usually used in those cases (though I could be wrong about this.)

747 aircraft can still have the 5th engine hardpoint installed as an option, even on the 747-8. Many foreign carriers that use the 747 still use this option if they don't have a huge spares network. Imagine the issues trying to get a GEnx engine from main MX base in Australia to London or LAX. It just makes sense to bolt the spare on another passenger flight and fly it there. The A380 doesn't have this ability.

Welcome to aviation.SE. We are not here to deliberate on what is "better", since that is a matter of personal opinions.

authors: Bob Jarvis - Слава Україні


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Have there been any solo flights on airliners?
As per subject has anyone flown an airliner (737, A319 etc etc or bigger) solo? (meaning only 1 pilot alone with no passengers?) Tried to google search but did not find any reference. Question applies to any of modern airliners era with and without flight engineer.

You can try, but perhaps with expect questionable results if untrained and understaffed ;)

@MikeFoxtrot - To be fair, there is some indication that the pilot in that instance was coerced and perhaps was struggling against his captor at various stages.  It might explain the outcome...

For a trained pilot, in most aircraft, it would be as easy as it would be illegal. Other than a nosewheel steering wheel or tiller, it is uncommon to have any vital control that can't be accessed from both seats. Not to say the solo pilot wouldn't be busy at times & wouldn't have his hands full if something failed, but as a matter of just getting from "A to B" it's not just possible to do solo, in many airplanes it would be pretty easy. Just thoroughly illegal, and accepting a lot of added risk if anything unusual happened.

@RalphJ Which is good, because pilots can get incapacitated, and so (in emergencies) a pilot may have to land the plane solo.

@MikeFoxtrot: It appears in that case, there was 1 "passenger".

Test flights? :)

It doesn't really meet your criteria, but I can't help but think of long oceanic legs in 747 freighters at night that the other pilot and the flight engineer were soundly asleep in their seats, and I was the only conscious person on the aircraft for an hour or more, often more. Some f.e.s would even leave their seat in favor of one of the first class seats still remaining on the upper deck or an installed bunk.

last week it happened :) https://www.independent.co.uk/news/world/americas/seattle-plane-crash-audio-hijacking-sea-tac-international-airport-a8487366.html

In normal operations there are regulations against this sort of thing (as Dave has said).  But there have been a few emergencies where the First Office or the Captain have become incapacitated (due to medical emergencies), and the remaining pilot has declined to ask if there is another pilot on board to help fly the plane.
Here is an example from 2011 of a Ryanair flight having this occur**, I have heard of others but can't find references.  So, admittedly, that may be the only actual occurrence.
So, to finally answer your questions:  Very rarely, in an emergency situation, there can be a single pilot on a commercial airliner.  Granted, there were passengers on board, so I'm not sure it fits your narrow definition of "solo", but it's about as close as it's going to get.

For completeness (though I don't think it counts), there have been a few instances of a single pilot stealing a commercial jetliner.
For example this 727.  There were actually two people involved, one was a mechanic, the other had a private pilots license (hence the pilot was "soloing").  The aircraft has not been seen since...so it's assumed it ended badly, and, for the record, it's also assumed the pilot was coerced (if indeed he was even flying the plane).
There are a couple more incidents, namely this Antonov-26, which was stolen by a mechanic, circled for an hour, then crashed.  And also this ATR-42-320, which was actually stolen by a Captain form Air Botswana.  He circled the airport for a couple of hours demanding to speak to everyone from his girlfriend, to his boss to the President of Botswana.  They were actually arranging to have him speak with the president when he crashed his plane into two other Air Botswana ATR-42-320s that were parked on the ground.  He was the only one killed.
Again, though, I'm not sure if these fit the criteria you are looking for.  But in that last one, at very least, he was the only person on board the aircraft, it was a commercial aircraft and he was in fact a Captain.
But to say all this an irregularity would be an extreme understatement...

** For clarification:  The reason I state this is the only example I could find is because it's the only one where I could find a report where it was specifically stated the remaining pilot had no help.  To quote from the report:

Once the initial Cabin Crew assistance was complete, the Captain indicated that he did not need assistance in operating the aircraft, although this was suggested in the operator’s procedures for pilot incapacitation. The First Officer took no further part in the operation of the aircraft. No inquiries as to the possible presence on board the aircraft of either medically trained personnel or qualified pilots were made.

All other examples I saw either specifically stated that a new co-pilot was found, or they skipped that detail entirely.
All of that being said, I somehow doubt this is the only case, it's just the only one I could explicitly verify.

These are accidents. They are technically valid even though to be honest I wanted to know if there were any purposely done flights but that were not with a bad "target" or intent such as the ones you described. (maybe NASA or other sort of tests) in any case very good answer.

@FabrizioMazzoni - I recognize this, and I noted it in the answer, but I figured that it would help to answer the title question, just incase someone stumbles in here wondering about any sort of commercial plane being flown solo for any reason.

Absolutely agree with you. That's why I even up voted the answer!

@FabrizioMazzoni Oh, thanks!  Always happy to be of some sort of tangential use ;) (it's what I'm good for.)

Even if the pilot does ask if there's another pilot, on a flight with not many passengers it's conceivable there wouldn't be another one on the plane. I'd be shocked if the Ryanair case was the only one.

This article lists several events in which a flight crew member was incapacitated. Surprisingly, in all but one of them, there was another pilot on board (granted, this was often a reserve pilot for the same airline, or, in cases of long-haul flights, a reserve pilot.) In two of the cases, the person who ended up helping out was a flight attendant who also had a pilot certificate. The case listed here where 1 pilot continued by himself was a 2010 Qatar Airways flight from Manila to Doha in an A330.

@cpast -  I'd also be shocked, it's just the one that I came across first and served as the example.  reirab seems to have dug up another one, I'm sure, as you said, that there are probably at least a few more.  It honestly isn't terribly common though, it takes several things going wrong to get to this point...

@reirab I can't seem to confirm that the FO flew the rest of the journey on their own in that flight?  Several articles say he "took over and diverted the flight", but I don't see any verifiable claims that he didn't have help.  In the Rynair case, it's recorded in the report that the FO specifically stated he didn't want the stewardess to ask if there was another pilot on board, that's why I used it as the example...

due to medical emergencies Or a missing windshield.

One more example of a single pilot for at least part of the flight:  Discovery Channel did a special that involved actually crashing a jetliner.  I do not recall the crew configuration at takeoff but I do recall that the bailout was handled in two stages, the pilot only going once everyone else was away.  The plane was being flown by remote control once he abandoned the controls.
This did not happen in the USA, as others have said it would be illegal.  Mexico allowed it with restrictions, though.

"as others have said it would be illegal" -- and I should think the US would take an even dimmer view of 0 pilots than they would of 1.

@SteveJessop The US routinely permits zero pilots--unmanned rocket launches.  That being said, I do not think the safety arrangements they had were adequate.  Since he only bailed once the plane was already aimed for impact I don't think the risk was high but I think it should have had a flight termination system and a lot more range on the control radio.

This was shown in the UK on Channel 4 and more details can be found here: http://www.channel4.com/programmes/the-plane-crash

As it was a test flight it would be legal with the right waivers and classifications.

OMG that documentary was terrible

Airplanes are certified to be operated with a particular amount of crew. From a regulation standpoint there are jets certified for single pilot operations but they tend to be on the smaller size (Citation Mustang comes to mind). That being said I cant say that these planes have never been flown in a single pilot situation.
This EU EASA document states that the minimum crew for a 737 is two

Minimum Flight Crew: Two (2): Pilot and Co-pilot, for all types of flight

The US type cert for the 737 says

Minimum Crew for All Flights: 2 (Pilot and Copilot)

which applies to all the following 737 models

DATA PERTINENT TO MODELS 737 Original Series -100, -200, -200C and 737 Classic Series -300, -400, -500:

So you could not do it in any kind of regular situation. It is possible that some of the planes were test flown with only a single pilot but I dont know for sure.

what about airshows?

@anshabhi at airshows you want maximum safety, so a full crew and maybe even an extra pilot as a backup.

This is not an answer.  The question is whether it has been done, not whether it was legal (assuming it has been done).

In the US part 25 aircraft (anything heavier than 12,500 lbs that isn't filed as a commuter-type) are assumed to be certified for dual-pilot operations.  I'm not sure if the FAA has ever made exceptions to this rule.  This would be the superficial reason why only smaller aircraft like GA aircraft are single-pilot certified.

There has been a televised test crash of a Boeing 727 that took place in Mexico.

The airplane took off from General Rodolfo Sánchez Taboada International Airport in Mexicali, with the flight crew and a small group of passengers, as well as a number of crash dummies, and with a chase plane following close behind. As the flight progressed towards the Sonoran Desert of Baja California in Mexico, its occupants parachuted to safety. Slocum was the last one to leave the jet, four minutes before impact. Shanle then flew the jetliner by remote control, from the chase plane.

This started out fully manned, but ended with the pilot being the last to leave the craft, after handing control over to a remote operator in the chase plane.

There was a precursor to this flight: a crash of a Boeing 720 (courtesy of Peter Kampf from the comments), conducted by NASA in 1984.
However, this likely does not fall into the criteria of your question, since the documentation seems to indicate that the entire flight was remote controlled. Or at the very least does not explicitly state solo piloting.

Yes I do remember that one. Brilliant documentary.

You might want to add the original crash test done by NASA in 1987 with a Boeing 720..

@PeterKämpf Done. However it may not be relevant to the question, since it seems to indicate that it was remotely piloted from the start.

Oh - I didn't know that. Then your 727 crash is really more relevant.

This procedure has been used as far back as WW2, when the USAAF and RAF tested it as a means to turn obsolete bombers into flying bombs. They'd take off with a minimal crew, the crew would bail out over friendly territory, and from then on the aircraft would be steered onto its target by radio control from another aircraft. I guess they didn't trust the radio controls they had to handle takeoff :)

@jwenting: With good reason, as, even with the takeoff being human-flown, only one of the flying bombs even got close enough to the target to cause damage (and even it missed by quite a bit, although it was packed with so much explosives that the blast did manage to damage the target) - details.

In summer 2018, 29-year-old Richard Russell, an airline ground agent, stole a Q400 twin-engine turboprop (which at least USA Today calls an "airliner"), flew it solo, and pulled off some impressive maneuvers before crashing the plane, in an apparent suicide.

Why wouldn't a Horizon Air Q400 be considered an airliner?

@rclocher3 the original question mentioned "737 or larger"

British_Airways_Flight_5390

An improperly installed windscreen panel separated from its frame,
causing the plane's captain to be blown partially out of the aircraft.
The co-pilot took control and performed an unassisted landing.

Had passengers on board

Apologies for having not read the question correctly nor noticed the date!! Late night..


text:
Adverse pitch on unstable aircraft's roll
In airplanes like the F-22, both the main wings and the tailerons provide (at least at subsonic speed) positive lift. My question is this: when performing a roll using all control surfaces asymmetrically, specially the tailerons, it seems that the longitudinal moment around the center of gravity wouldn't be zero, since one of the tailerons goes down, so the aircraft should tend to pitch (up) adversely. Is this true?
I guess the surfaces don't move completely asymmetrically but in a differential fashion, so the up going taileron moves further up to compensate for the negative lift of the down going taileron, or maybe the forces distribution is such that this is negligible. Also I'm disregarding important effects like drag.
So, does this adverse pitch may really happen?

If differential displacement causes a pitching reaction that is not what is being called for by the pilot at a given time, the computers will simply adjust the differential positions to compensate.  It's all going to be going on continuously in the background.

I understand that the forces probably aren't perfectly symmetrical, but I'm curious why you wouldn't assume that they would mostly cancel each other out?  My presumption is that equal and opposite deflection would simply result in a nice tight spiral, with little to no pitching moment.  What makes you think it would pitch up?

Well, in stable flight, both tailerons generate positive lift. Jut by one taileron going neutral (cero AOA) an thus generating no lift, the longitudinal moment around the center of gravity wouldn't be cero. If that surface goes even further down generating negative lift, the unbalance would increase even more. So the up going taileron needs both to compensate this and generate the necessary additional lift to maintain longitudinal stability. Pure asymmetric movement can't achieve this, I guess. But well, as everybody has said, computers will take care of this.

But positive lift or negative lift, if the roll is initiated when the pitching moment is zero, then they are both moving opposite each other from a neutral position, right?  And if one needed to travel further than the other to avoid a pitching moment it seems engineers could compensate mechanically too.

Yeah, but my point was that neutral position is not cero angle of attack, but a positive one, so there is a "lift bias" (may I say it like that?) that has to be compensated. Anyway, like you and Koyovis have mentioned, any compensation can be mecanically enforced too, pretty cool indeed. By the way, happy new year!

Pic above is a still @ 1:37 of this video, of a model F-22, and shows the ailerons and the all-flying tail deflecting to command a roll. Both ailerons and tailerons can be commanded such that there is no resulting pitching moment: negative lift of the one end is exactly the positive lift of the other end, cancelling each other out. This is not necessarily at symmetrical deflections, no problem for the flight control computer of the real aircraft.
From the wiki:

Flight control surfaces include leading-edge flaps, flaperons, ailerons, rudders on the canted vertical stabilizers, and all-moving horizontal tails (stabilators); for speed brake function, the ailerons deflect up, flaperons down, and rudders outwards to increase drag.

So all flight control surfaces can be commanded individually, and a feedback loop from the motion sensors will position the matrix of surfaces such that only a roll rate results. Also compensating for:

Adverse yaw, which is not a very dominant effect in short wing span fighters.
Inertial coupling, where the nose starts to point in increasing circles at sustained high roll rates.

The all flying tail surfaces can superimpose a symmetric (pitch axis) deflection upon any asymmetric (roll axis) deflection, compensating for any unwanted pitch accelerations. Even without a flight control computer the pitch and roll can be uncoupled mechanically, like in the 4-DoF helicopter mixers.

Well, maybe my question was more like "can this effect happen?", but since these computer-driven machines are another kind of beasts there has to be a lot of things the computers compensate for like the two things you mentioned. Thanks everybody!

That's really cool. I really like the power of electronics, but being able to achieve such things mecanically is just so pleasant. Happy new year!


text:
Could MH370 happen again today?
This month being the 10th anniversary of the tragedy that shocked the world, Malaysia Airlines Flight 370, I wonder if this could happen again today.
Can I pilot of a airliner make an airplane "disappear" and make it impossible for recovery?
I can't recall any new changes that were implemented after the tragedy, were there any?

I can't recall any new changes that were implemented after the tragedy, were there any? https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_370#Air_transport_industry The Wikipedia page has it neatly summarized for you.

This doesn't answer the question literally because it's not changes that were implemented but rather changes that "just happened", but the price of building satellites has dropped significantly since then, as has the price of operating satellites, and most dramatically, the price of launching satellites has come way down. The number of active, operational satellites in space has increased by a factor of 7.5 between 2014 and now and is only going to grow.

Of the ~17000 objects that have been launched into space by all of humanity combined in the last 66 years, almost half have been launched in the last 4 years. And one fourth of all satellites launched in the history of humankind are Starlink satellites, which enable high-bandwidth, low-latency, reliable data communication everywhere on Earth – something that simply did not exist 10 years ago. And they're not the only ones, there's OneWeb, Project Kuiper, two private and one military Chinese network, Starshield, …

All of these are significant changes, but none of them have been implemented. They just happened.

@JörgWMittag, it doesn't answer the question because it isn't an answer... it's a comment.  Anyway, Sanchises didn't claim that the changes came about as a direct result of this flight, only that changes have occurred.  It was simply an offer of information.  Oh yeah, and satellite launches don't "just happen"!

"Space-Based ADS-B: No longer a concept, but an operational reality" by Aireon. Apparently they have a contract with Eurocontrol. They seem to use the Iridium constellation.

@mins Space-Based ADS-B is pretty interesting, especially for oceanic airspace, but it won't help when the transponder is intentionally turned off like it was on MH370.

@Bianfable: Space ADS-B is a required condition to save lives and spare money/time in avoidable SAR (AF447). This condition is going to be a reality (the data volume is very low, not a concern for satcoms), but is not sufficient. It's more than urgent for the regulating agencies to make crews admit the necessity to remove the possibility for them to disconnect safety devices. Technically it is a trivial change, and there is no valid excuse. A lot of electrical devices cannot be disconnected already (e.g. the ELT).

so from what I read, that means technically, as of today, the same thing can happen again?

@Gabe: Can this happen again? It depends on what you put behind "this", we are still reduced to conjectures.. ADS-B, ACARS  and radar contact could still be lost over ocean. Nothing indicates events like switching off radio signals are deliberate actions.The scenario of a lithium fire followed by a depressurization and/or general hypoxia is one of a few credible scenarios. On the changes side, it is possible MA has now subscribed for a satellite link for ACARS on all of its aircraft flying over the ocean. If this is the case, ACARS may be sufficient to locate the plane.

@mins - other scenarios maybe are technically possible, but the circumstantial evidence surrounding the turnaround seems just short of conclusive that it was likely intentional. Mentour Pilot recently posted an interesting video about it.

@StevePemberton: I agree, since 2018 and the investigation report, it's established the turn at IGARI was made in manual control. That can be criminal or the result of a catastrophic event, without the faintest element in favor of one direction.


text:
Are there any manoeuvres that would be considered unrecoverable in a General Aviation / Training Aircraft?
I'll try to make this question a little more manageable by applying the following constraints, though of course all answers would be welcome:

By "General Aviation / Training" aircraft, I'm talking primarily about normal SEP's of the kind that we see daily and would require no more than a check-ride before hiring. No experimentals, warbirds, super rare aircraft etc - though MEP's and Complex Aircraft would count.
I'm ignoring low level maneuvers. We all know a stall at 100ft is going to be tricky, though on the other hand, if something is going to require 5000' at a minimum to recover from then that's going to be fatal in most cases.
Let's ignore mechanical and airframe failures that occur prior to the incident.
I'm assuming Weight & Balance are within the normal category of the POH (As opposed to utility or aerobatic).

Beyond that, the question is what it says on the tin. Is there anything stupid that I can do as a Pilot in a Single Engined Piston GA aircraft that I simply won't be able to recover from, even with a few thousand feet to do so?

What about the pilot? Are you including things like freezing up on the controls, trying maneuvers you haven't been trained for, knowingly exceeding the aircraft's limitations etc.?

I would think anything beyond a second or two of inverted flight will cause "most" GA aircraft problems, although potentially not irrecoverable.

Engine out in certain parts of some flight envelopes.
Rotary wing - may be outside your intended group: Failure to enter autorotation within model specific period after ;loss of all power - varies widely and for eg Robinson R22 and similar it's about 1 second!. Many are substantially longer.
Take off in ground affect in a combination of conditions that pure flight is not possible, then leave ground affect region :-(. This kills numerous people who overload craft so that they can fly in WIGE mode but not "properly". Once you terminate GE you are flying a stone.

Autogyro - probably doesn't meet your requirement: Create negative g on rotor (eg climb then level out and descend  rapidly so that rotor ends drop into unintended area and strike eg tail structure. (Happens :-(.) || Happens more in warbirds BUT perform takeoff in rotary engine craft (1st catch your rotary engined craft :-) ) and compensate for torque rotation in wrong direction! :-(.  eg Merlin Spitfire and ?Sabre? engine had opposite rotation directions. A spitfire was destroyed here and pilot very severely injured due to this. (Torque is due to very large engine rotating mass).

Specifics escape me (I am NOT a pilot!)  please excuse really lame description (and any above :-) ). I understand that there is a known problem turning across a circuit with wind in a certain direction that traps newcomers.

Some versions of entering turbulence behind larger aircraft - loss of US airliner (New York) some years ago attributed to this. || If wind-shear gets the professionals and ideally needs wind rRADAR surely it must affect amateurs too?.

Yes, easily. Just fly fast enough.
If you deflect a control surface fully at a speed above $v_A$, the risk of a structural failure is very real. After all, at $v_D$ only a third of the mechanically possible deflection is allowed (see §23.441 for the rudder and §23.455 for the ailerons). Even combining full deflections of more than one control surface at $v_A$ is not covered, as is a repeated deflection in sync with rigid body oscillations which can create excessive loads. For a definition of the design speeds, see §23.335.
The regulations require minimum control forces so the pilot feels when he/she overstresses the airframe, but they are still within the strength of a normal adult.
Also, if you fly too fast in gusty weather, you can overload the structure. This is rare because the 25ft/s gusts which must be tolerated up to $v_D$ are quite uncomfortable to fly through.

Naive question: By v_C and v_D do you mean "Design Cruise Speed" & "Design Driving Speed"? That's what Wikipedia tells me for this notation. https://en.wikipedia.org/wiki/V_speeds#cite_note-faacfr-7

@curious_cat: Yes, exactly.

@curious_cat: Your question made me note that I confused v$_C$ with v$_A$. Silly me.

There also has to be a steep descent, otherwise you could just reduce thrust. And even if there is a steep descent, it could be recoverable with 10% deflection, well above Vd.

I'm pretty sure this is not the kind of "maneuver" you're looking for, but it is

something stupid that I can do as a Pilot in a Single Engined Piston GA aircraft that I simply won't be able to recover from.

CAPS deployment in an SR-20/22 is unrecoverable - once the chute is out, there's no putting it back in.

"Unrecoverable" is too ambiguous: ending in rapid unscheduled disassembly, unimproved field takeoff,  knucle-busters and JB Weld, GPS ELT activation, hitchhiking or Uber.

The two most common training aircraft out there are the Piper Cherokee (numerous variants) and the Cessna 172/152 (numerous variants as well). The cherokee is not spin certified and the 172 is only spin certified in the utility category so I would not try spinning either frankly. Technically you may be able to recover from a spin with enough altitude and depending on the situation but a pilot could get them selves into a nasty situation by spinning either plane. Even regular stalls put you at risk of entering a spin.
There are lots of maneuvers (aerobatic mainly) that would kill the engine on many common GA planes. Generally speaking the oil systems are not built for inverted maneuvers or anything that would starve the oil pump. The Cessna also has a gravity fed fuel system which would not do to well inverted. In regards to stalling the engine and recovering while you may be able to glide down to a field if an engine is lost this is more in reference to losing an engine during a maneuver and having insufficient thrust to recover properly from the maneuver.
I would think that you might also be able to get the plane into an aggressive dive that might be hard to recover from for an untrained pilot. At some point the recovery will exceed the load the wings can handle as well.
Here in the US the FAA requires knowledge of spin awareness and what may cause a plane to enter a spin but there is no requirement to demonstrate a spin for a basic private pilots license nor is there a requirement for them to be demonstrated to the student.

I'm not sure I'd describe engine failure as unrecoverable, since it's still possible to glide to a handy field and make an emergency landing. It's something we're all trained for.

Is it not thought essential to expose trainee pilots to spins? How about stall training (if the risk of a stall turning into a spin is high).

@curious_cat See this question for information about stalls. Training requirements depend on the local regulations; the US requires spin training only for instructors, for example. It could be a good question if you want to ask it.

172s are a pain to spin.  you need an aggressive entry and they decay into steep spirals quickly.  More danger in late recovery from the spiral dive over-stressing the airplane than the spin itself.  @curious_cat private pilots just need to learn what an incipient spin feels/looks like, how not to get that far into one and how to recover from a spin, but they don't actually spin.  Spin demonstrations aren't required until you get your CFI. (FAA)

@casey Yes, that's exactly what I had always thought. That 172's are a pain to spin. But I was confused on reading what wrote above. i.e. "Even regular stalls put you at risk of entering a spin" I always thought even if one wanted to foolhardily, putting a 172 into a spin needed some pretty bizzare antics?

Yup. Most GA engines' fuel systems are gravity fed, whereas aerobatic planes can pump fuel from tanks, send it pressurized from nearly any orientation and G-loading and not have carbs hydrolock or suck air. Reminds me of the fuel restrictor plate hack on the Spitfire and Hurricane. (Miss Shilling's orifice... no joke.)

@Dave FYI, Cherokees are spin certified if the weight and balance falls into the  Utility category. Mine even has a placard on the dash listing entry speeds for spins, lazy eights, and chandelles.

@JScarry interesting, all the ones i have flown have "Do Not Spin" placards but i guess its possible the flight schools put them in to prevent dangerous operations.

@Dave Mine is an older one, so they may have changed it. Check out Page 23 https://touringmachine.com/Cherokee/PDFs/Cherokee%20140%20Owner's%20Handbook.pdf

@JScarry I did a lot of time in warriors which are ok for chandelles and lazy 8's but spins are not aloud in any category i guess its technically not a Cherokee but i always lumped it in as it is a PA-28

Yes indeed.
AD 69-24-04 PIPER increases the Vmc speed of the Twin Comanche by 9 knots because the aircraft was discovered to enter an unrecoverable flat spin when stalled near Vmc.  Always a bummer when that happens.

Some bad ones:
Stalling while turning too abruptly at low speed and low alt < 500', but above ground effect height, cartwheeling to your death. Ideally, a ballistic parachute system should optimize for this, but too much of a spin component may twist/collapse the chute of some designs from opening soon enough.
Losing power after takeoff but then trying an impossible 180° turn back when the safest plan is to dead-stick to anything remotely flat ahead.
Ripping wings off from too aggressive maneuvers plus repeated fatigue cycles of old/worn planes performing aerial firefighting without sufficiently-thorough metallurgical inspections (NDT). There was that Herc that sadly bought it on viceo.
Far exceeding Vd and causing structural failure from control surface, harmonic resonant and/or structural overload.
Mach tuck on the early P-38, Hawker P.1081 and other late, fast WW2 aircraft. Maybe they could sometimes recover with very careful dirty config and throttling back, but nosing over while transonic risks an unCFIT situation very quickly.